As the compounds exhibiting antihypertensive activities due to ACE inhibitory activities, there are known indan derivatives represented by the formula ##STR2## [wherein R.sup.2 stands for a lower alkyl group (preferably methyl group), R.sup.3 stands for an aralkyl group (preferably phenethyl group) and R.sup.4 stands for a lower alkyl group (preferably ethyl group), and the asymmetric carbon atoms designated (*1) and (*2) are both desirably in (S)-configuration] and salts (preferably hydrochloride) thereof [Japanese Unexamined Patent Publication No. 57-77651; Japanese Unexamined Patent Publication No. 57-179141; Chem. Pharm. Bull, 34, pp. 2852 (1986)].
In Japanese Unexamined Patent Publication No. 57-77651 and Japanese Unexamined Patent Publication No. 57-179141, the following method is described as a typical one for preparing the compound (Ia). ##STR3##
(Upon necessity)
[wherein R stands for hydrogen or a lower alkyl group]
In the above method, the compound (Ia) is usually obtained as a mixture of two kinds of steric isomers (asymmetric carbon of *2). Therefore, for obtaining a desired optically-active compound, it is necessary to resort to, for example, optical resolution.
In Chemical and Pharmaceutical Bulletin, 34, p. 2852 (1986), the following method is described. ##STR4##
The above method comprises condensation of the compound (V) with (VI) in the presence of diethyl phosphorocyanidate (DEPC). This method has some problems from the industrial viewpoint in that highly toxic DEPC is used, and that hydrogen cyanide is generated by the hydrolysis of DEPC and further that the yield is not high (yield: 68%).
And, in Japanese Unexamined Patent Publication No. 57-176941, the following method is described. ##STR5##
The above reaction yields the compound (IX) by allowing the compound (VII) to react with an acyl derivative of the acid represented by the formula (VIII) under amide-forming conditions. This method also has some problems from the industrial viewpoint in that use of an acyl derivative of the compound of the formula (VIII) is required and that the yield is not high (yield: 69.7%).